The present invention relates to a lubrication system for an electric apparatus journalled by means of sliding bearings. To be more specific, the invention relates to an electric apparatus that includes an end N at which is located a fan and an end D at which is located a shaft, and a rotor which is journalled at one end by means of a first sliding bearing at the end N and at its opposite end by means of a second sliding bearing at the end D, the end N being provided with a first bearing housing with an oil sump for the first sliding bearing and the end D being provided with a second bearing housing with an oil sump for the second sliding bearing.
Electric apparatuses of the described type are largely known. As rotational speed or ambient temperature increases, the warming up of electric apparatuses may cause problems. The temperature of sliding bearings may rise too high as regards the operation of the bearings, wherefore limits are set regarding the highest operating temperatures of bearings. The warming up of the bearings is a result of the transference of the heat originating from the rotor to the bearings and of bearing friction. Even if the bearings comprise an oil scraper ring, it is not sufficiently capable of lifting colder oil from the lower part of the oil sump to the bearing area to efficiently cool the bearings. In rib-cooled electric apparatuses, the problem is further aggravated by the fact that cooling air passes from the end N to the end D through the ribs past the bearing located at the end D. The cooling air departing from the end N is thus warmed in the cooling ribs while propagating towards the end D, and the cooling capacity thereof essentially deteriorates before it has reached the bearing of the end D. For the reasons mentioned, the difference in temperature between the bearing applications of the end D and the end N is significant.
Experiments have shown, for instance, that for a rib-cooled squirrel-cage motor, the capacity of which was 300 kW, rotational speed 3577 revolutions per minute, frequency 60 Hz and the number of poles 2, the highest temperature at the end D in the bearing was 78.5.degree. C. at ambient temperature of 23.5.degree. C., whereby the warming up of the end D was 55.degree. C. The maximum warming up specified for the motor was 50K, this value being thus exceeded. Correspondingly, the warming up of the end N was 39.4.degree. C. The difference in temperature of the bearings in the end D and the end N was 15.6.degree. C.